Computational Investigation of the Lewis Acidity in Three-Dimensional and Corresponding Two-Dimensional Zeolites: UTL vs IPC-1P

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 118; no. 35; pp. 7526 - 7534
• Main Authors: Thang, Ho Viet, Rubeš, Miroslav, Bludský, Ota, Nachtigall, Petr
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04.09.2014
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp501089n

The adsorption and catalytic properties of three-dimensional zeolite UTL were investigated computationally along with properties of its two-dimensional analogue IPC-1P that can be obtained from UTL by a removal of D4R units. Adsorption properties and Lewis acidity of extra-framework Li+ sites were investigated for both two- and three-dimensional forms of UTL using the carbon monoxide as a probe molecule. The CO adsorption enthalpies, calculated with various dispersion-corrected DFT methods, including DFT/CC, DFT-D2, and vdW-DF2, and the CO stretching frequencies obtained with the νCO/r CO correlation method are compared for corresponding Li+ sites in 3D and 2D UTL zeolite. For the majority of framework Al positions the Li+ cation is preferably located in one of the channel wall sites and such sites remains unchanged upon the 3D → 2D UTL transformation; consequently, the adsorption enthalpies become only slightly smaller in 2D UTL (less than 3 kJ mol–1) due to the missing part of dispersion interactions and νCO becomes also only up to 5 cm–1 smaller in 2D UTL due to the missing repulsion with framework oxygen atoms from the opposite site of the zeolite channel (effect from the top). However, when Li+ is located in the intersection site in 3D UTL (about 20% probability), its coordination with the framework is significantly increased in 2D UTL and that is accompanied by significant decrease of both νCO (about 20 cm–1) and adsorption enthalpy (about 20 kJ mol–1). Because the intersection sites in 3D UTL are the most active adsorption and catalytic Lewis sites, the results reported herein suggest that the 3D → 2D transformation of UTL zeolite is connected with partial decrease of zeolite activity in processes driven by Lewis acid sites.